1. Field of the Invention
The present invention relates to a transmitting and receiving circuit for transmitting and receiving data, and also relates to a semiconductor device including a transmitting and receiving circuit for transmitting and receiving data.
2. Description of the Related Art
In recent years, an individual identification technology using wireless communication (hereinafter referred to as a wireless communication system) has attracted attention. In particular, as a data carrier which communicates data by wireless communication, an individual identification technology using an RF tag (hereinafter collectively referred to as a semiconductor device regardless of the shape such as a card shape or a ship shape) utilizing RFID (Radio Frequency Identification) technology has attracted attention. The semiconductor device is also called an IC (Integrated Circuit) tag, an IC chip, an RFID tag, an RF tag, a wireless tag, an electronic tag, or wireless chip. The individual identification technology using a semiconductor device has been useful for production, management, or the like of an individual object, and application to personal authentication has been promoted.
The term “wireless communication system” here refers to a communication system for transmitting and receiving data between a receiver-transmitter with a power supply source, such as a reader/writer, and a transmitter-receiver such as a semiconductor device.
In such a wireless communication system, a reader/writer and a semiconductor device are not necessarily physically connected to each other. That is, the reader/writer can communicate with the semiconductor device so that data can be transmitted and received to/from the semiconductor device, as long as there is the semiconductor device in a region designated by the reader-writer.
Semiconductor devices can be broadly categorized into two types: active semiconductor devices and passive semiconductor devices. An active semiconductor device incorporates a primary battery and operates by obtaining a power supply potential from the battery. Meanwhile, a passive semiconductor device does not incorporate a battery. A passive semiconductor device generates a power supply potential therein by using a wireless signal from a reader/writer and operates with the power supply potential.
In a wireless communication system, when data is transmitted and received between a reader/writer and a plurality of semiconductor devices at the same time, distances between the reader/writer and the plurality of semiconductor devices (hereinafter referred to as a communication distance) are not completely the same. There may be a case where a communication distance varies from hour to hour; for example, products to each of which a semiconductor device is attached may be packed in a carton, be put on a forklift, and pass in front of a reader/writer.
A wireless signal transmitted by a reader/writer attenuates in proportion to the square of a distance between the reader/writer and a semiconductor device. The amplitude of a wireless signal fluctuates in accordance with power received by a semiconductor device. Therefore, power to be supplied to a semiconductor device from a reader/writer varies depending on a communication distance.
Therefore, in a wireless communication system using a passive semiconductor device, when a reader/writer and a semiconductor device are away from each other and thus a communication distance is long, only weak power is supplied to the semiconductor device.
Since a passive semiconductor device needs a certain level of power for normal operation, in the case where a semiconductor device can receive only weak power, the semiconductor device cannot generate a power supply potential needed for operation and thus cannot operate.
A communication distance has a relation to a performance of a transmitting and receiving circuit of a semiconductor device. A communication distance can be extended by improvement of efficiency in conversion of power received by a transmitting and receiving circuit into a power supply potential or DC power (hereinafter referred to as power conversion efficiency). The above-described transmitting and receiving circuit has a rectification function for converting a received power of a wireless signal (hereinafter referred to as received power) into a power supply potential, a demodulation function for extracting data from a wireless signal, and a modulation function for changing an input impedance of a semiconductor device by changing an input impedance of a transmitting and receiving circuit, and then transmitting data.
An active semiconductor device incorporates a primary battery. An active semiconductor device can operate regardless of a communication distance while a charge is in a primary battery and cannot operate when no charge is therein.
As applications of active semiconductor devices and passive semiconductor devices, semiconductor devices each incorporating a secondary battery have been developed. Power conversion efficiency of a transmitting and receiving circuit in the case of a semiconductor device incorporating a secondary battery affects time for charging a secondary battery and the level of power for charging. Therefore, in the case of a transmitting and receiving circuit as a semiconductor device incorporating a secondary battery, reduction in charging time or storage of weaker charging power can be achieved by improvement of power conversion efficiency.
FIG. 6 shows a conventional transmitting and receiving circuit of a semiconductor device (see Patent Document 1: Japanese Published Patent Application No. 2002-152080). A transmitting and receiving circuit 626 of the semiconductor device shown in FIG. 6 has a circuit configuration in which a voltage doubler rectifier circuit 602 having two stages and a voltage doubler rectifier circuit 603 having two stages are connected in parallel. The voltage doubler rectifier circuit 602 includes an input terminal 600, an input terminal 601, an output terminal 613, four transistors, and four capacitors. In the transmitting and receiving circuit 626, the voltage doubler rectifier circuit 602 has a rectification function and outputs a DC potential obtained by rectification of an AC signal inputted from the input terminal to the output terminal 613. Further, in FIG. 6, the voltage doubler rectifier circuit 602 is additionally provided with a transistor 604 and a transistor 605 and is controlled by a terminal 607 so that a modulation function is provided.
On the other hand, in FIG. 6, the voltage doubler rectifier circuit 603 includes the input terminal 600, the input terminal 601, an output terminal 623, four transistors, and four capacitors. In FIG. 6, the voltage doubler rectifier circuit 603 is connected to a transistor 606 so that a demodulation function is provided. In the voltage doubler rectifier circuit 603 provided with a demodulation function, which is shown FIG. 6, the transistor 606 needs a bias terminal 624. A given bias voltage in accordance with a voltage value of the output terminal 613, which is a power supply potential, is supplied to the bias terminal 624 so that a current load in proportion to a consumed current of a circuit of a next stage, which is the load of the voltage doubler rectifier circuit 602, can be achieved.
In FIG. 6, with the voltage doubler rectifier circuit 602 provided with a modulation function and the voltage doubler rectifier circuit 603 provided with a demodulation function, the transmitting and receiving circuit 626 achieves a rectification function for converting a received power into a power supply potential, a demodulation function for extracting data, and a modulation function for transmitting data.